Suspension

One of the problems with having long rigid wheelbases in O gauge coupled with wheels with tiny flanges is the propensity of said vehicles to leave the rails at their earliest convenience. Assembling them on a flat surface such as a piece of glass might feel nice but it only works if the track never deviates in height over the length of the wagon by less than the height of the flange. Given my layout will be mainly outdoors the chances of never having such deviations is wishful thinking. Visits to other layouts with larger flangeways can also test your models out.
There are many proprietary rocking and sprung systems on the market, however such items don't really fall into this railway's budget. Just removing the bearings added some flexibility that solved some situations but didn't solve everything. Replacing the bearings in one end and adding two springs to bear down on the other axle without bearings seems to have made a very reliable vehicle. The 3 versions I have so far made stay on the track no matter the deviations I have made to test them.
These are all assembled wagons that I have been retro fitting. For my new wagons I might be able to keep the bearings on all wheels and just deepen the bearing hole downwards to allow some vertical movement.

The above photo shows the two pieces of brass wire inserted into the floor of the S wagon. Wire is either 15  or 22 thou depending on what I had in stock. In this case I melted the wire into the urethane with a soldering iron and set it with superglue. Tension is adjusted to be just enough to lift the wheels when upside down. A coat of black paint will make them all but invisible from normal viewing distance. If this suspension system proves itself over time I will have solved one of my biggest concerns since changing from AMRA wheel and track standards.